Various kinds of blood treatment apparatuses are known. The known blood treatment apparatuses include, for example, the apparatuses for haemodialysis, haemofiltration and haemodiafiltration. During the blood treatment, the patient's blood flows in an extracorporeal blood circuit through a blood treatment unit. In the case of the apparatuses for haemodialysis, haemofiltration and haemodiafiltration, the blood treatment unit is a dialyser or filter, which is separated by a semi-permeable membrane into a blood chamber and a dialysing fluid chamber. During the blood treatment, the blood flows through the blood chamber, whilst the dialysing fluid flows through the dialysing fluid chamber. An effective blood treatment requires that blood and dialysing fluid flow in opposite directions along the membrane of the dialyser or filter. In the case of a flow in the same direction, the blood treatment is less effective.
The dialyser or filter is an interchangeable unit, which is connected to the fluid system of the blood treatment apparatus. The fluid system of the known blood treatment apparatuses comprises a line system with a first and a second line segment for the connection of the blood treatment unit. For the connection of the dialyser or filter to the fluid system, the first line segment is connected to the inlet of the dialysing fluid chamber and the second line segment is connected to the outlet of the dialysing fluid chamber of the dialyser. The connection of the dialyser takes place with known connection pieces, which include the known Hansen couplings.
The manufacturers of dialysers and blood treatment apparatuses provide a colour coding of the inlet and outlet of the dialyser and of the Hansen couplings to be connected to the inlet and outlet, in order to make it easier for the user to make the correct connection according to the counter-flow principle. This colour coding, however, is not uniform with all manufacturers. There is therefore the risk of the connections being confused, which will be referred to below as an incorrect connection. The effect of this is that the dialyser is not operated with a counter-flow. Consequently, the effectiveness of the treatment for the patient is inadequate. This is problematic, inasmuch as an incorrect connection of the dialyser may possibly remain unnoticed. In principle, therefore, there is the risk of the patient being treated with inadequate efficiency over a long period.